Activated carbon materials have found use in a variety of applications in the gas phase such as for example radon testing, gas masks, adsorption of volatile organic compounds, etc.
The predominant commercial use for activated carbon is in the form of granules. While activated carbon in the form of granules can perform the desired adsorption for many applications, there are some applications in which the granules have drawbacks. In some cases back pressure of a packed bed of granules is a problem. Some applications can result in considerable wear of the granules by attrition, causing loss of material or bed packing. Furthermore, the fines which are generated as a result of attrition can block the flow path.
Another approach is to use an extruded activated carbon in the form of a cellular structure such as a honeycomb. The honeycomb can readily be shaped by extruding fine powders of activated carbon with suitable binders. Such a shape allows for ease of flow of the gases through the honeycomb with little back pressure. Also, since the honeycomb is a solid piece, there should be little or no wear or attrition of the carbon.
In order to form an activated carbon honeycomb by extrusion, the carbon must be in the form of a fine powder. This can then be mixed with a liquid such as water and suitable plasticizers and binders. This plasticized mixture is then extruded through a die into the honeycomb shape, and dried.
These bodies sometimes suffer from low strength both in the as-extruded state and in the as-dried state. They can also develop cracks during the drying procedure. This is especially evident in the larger bodies due to differential shrinkage which occurs because of loss of moisture between the outer surfaces and the interior of the body.
Clays have been used as binders in carbon mixtures to impart strength to the carbon body formed therefrom.
U.S. Pat. No. 4,518,704, JP 57-122924 (1982), and 49-115110 (1974) relate to bodies containing or made of activated carbon in which clay binders are used.
It is highly desirable to improve the strength of the extruded honeycomb both in the extruded state for further processing and handling and also after drying to improve performance. The present invention provides such improved bodies and a method for making them.